Garrus is one of the best romances for female Shepard. I would choose him in all my gameplays, but there are other cute romances for femshep, like Liara and Thane. Garrus romance in ME2 isn't the cutest because is first based in "blow of steam", but in ME3 Shep and Garrus can really love each other. Thane romance in ME2 is super cute, but in ME3 is too tragic and can break everyone's heart. Liara romance is a little forced because Bioware really wanted you to be with her, but, otherwise, is very well developed and cute. I don't know about Kaidan romance, but there are people who like it. Jacob romance is the worst in my opinion and that isn't because of Jacob's hateful personality (I won't spoiler you). I recommend you don't choose him.

Just a suggestion for ME3, Garrus aside (the dude is on a whole different league of awesome), I would go with Kaidan if you want to feel a connection. Kaidan is a bro if you play right, and he often shares his intimate thoughts with Shepard and understands (while Garrus seems to calm Shepard's nerves and shares insecurities).

Also, you mentioned VANGUARD Shep, my favorite class of all. Kaidan is a perfect squadmate for Vanguard, with his Reave that can affect multiple opponents in a row, allowing your Charge and Nova to absolutely DESTROY enemy groups. He also comes equipped with tech attack to compliment Vanguard Shepard dealing with shields. He has Barrier, allowing him to survive close range battles with tough enemies like Banshee, Brutes...

Story-wise, I think a Vanguard Shep and Kaidan, both being human biotics, could have a lot things to talk about.